Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.39   11.753%   $63.0175   $63.02   $63.00   $63.00  
  Purchase #2 $138.96   9.602%   $152.3029   $152.30   $152.30   $152.30  
  Purchase #3 $31.80   10.354%   $35.0926   $35.09   $35.10   $35.10  
  Purchase #4 $217.61   11.367%   $242.3457   $242.35   $242.35   $242.30  
  Purchase #5 $69.83   13.318%   $79.13   $79.13   $79.15   $79.10  
  Purchase #6 $121.55   9.742%   $133.3914   $133.39   $133.40   $133.40  
  Purchase #7 $79.94   12.257%   $89.7382   $89.74   $89.75   $89.70  
  7 purchase totals = $716.08       $795.0183   $795.02   $795.05   $794.90